1. Field of the Invention
This invention concerns a light valve system and, more particularly, a light valve system utilizing particulate material as a medium for restricting light transmission through the valve.
2. Description of the Prior Art
Greenhouses provide weather protection for tender plants. Cultivation of the plants requires the atmosphere within the greenhouse to be maintained at a selected temperature and humidity level. Factors affecting the greenhouse atmosphere include heat gains and heat losses. For example, during long periods of sun exposure, abnormal amounts of solar energy enter the greenhouse which tends to raise the temperature. Heretofore the exterior surfaces of the greenhouse have been painted, for example with whitewash, to restrict transmission of solar energy into the greenhouse; and sometime thereafter the whitewash has been removed to restore the original light transmission character of the greenhouse walls and roof.
Where excessive outward heat radiation is encountered, such as during cool clear nights or during winter, abnormal heat losses occur which tend to lower the temperature within the greenhouse. Such losses have heretofore been reduced by covering the greenhouse with a tarpaulin or other suitable insulating covering.